Singlet oxygen and other oxidation (superoxide, hydroxyl radical) reactions of model biological substrates (histidine, tryptophan, guanosine, ascorbic acid and tocopherols) will be studied. Primary photooxidation products and mechanisms of reactions will be determined. The yield of singlet oxygen from the dismutation of superoxide will be determined using specific chemical traps. The mechanism of leucocyte action will be studied. Reactive intermediates in catechol oxidation will be determined.